C语言：输入年月日判定为当年的第几天(C language: enter the year, month and day to determine the day of the year)

#include<stdio.h>
main()
{ 
 int year,month,date,x=0,t=0;
 printf("请输入年份：");
 scanf("%d",&year);
 printf("请输入月份：");
 scanf("%d",&month);
 printf("请输入几号：");
 scanf("%d",&date);
 printf("\n");
  month=month-1;
 if((year%4==0&&year%100==1)||year%400==0) t=1;
 switch (month)
 {
  case 11: x=x+30;
 case 10: x=x+31;
 case 9: x=x+30;
 case 8: x=x+31;
 case 7: x=x+31;
 case 6: x=x+30;
 case 5: x=x+31;
 case 4: x=x+30; 
 case 3: x=x+31;
 case 2: x=x+29;
 case 1: x=x+31;
}
if (t==0 && month>1) x=x-1;
 x=x+date;
 printf("为本年的第%d天",x);
}
#include <stdio.h>
main()
{
    int year,month,two,day,sum=0;//two代表2月 
    printf("请输入年份:"); 
    scanf("%d",&year);
    printf("请输入月份:");
    scanf("%d",&month);
    switch(month)
    {
        case 1:sum=0;break;
        case 2:sum=31;break;
        case 3:sum=59;break;
        case 4:sum=90;break;
        case 5:sum=120;break;
        case 6:sum=151;break;
        case 7:sum=181;break;
        case 8:sum=212;break;
        case 9:sum=243;break;
        case 10:sum=273;break;
        case 11:sum=304;break;
        case 12:sum=334;break;
        default:printf("输入错误"); 
    }
    printf("请输入日:");
    scanf("%d",&day);
    sum=sum+day;
    if(year%4==0&&year%100!=0||year%400==0&&month>2)
    sum++;
    printf("今天是%d年的第%d天\n",year,sum);    
 }
————————
#include<stdio.h>
main()
{ 
 int year,month,date,x=0,t=0;
 printf("请输入年份：");
 scanf("%d",&year);
 printf("请输入月份：");
 scanf("%d",&month);
 printf("请输入几号：");
 scanf("%d",&date);
 printf("\n");
  month=month-1;
 if((year%4==0&&year%100==1)||year%400==0) t=1;
 switch (month)
 {
  case 11: x=x+30;
 case 10: x=x+31;
 case 9: x=x+30;
 case 8: x=x+31;
 case 7: x=x+31;
 case 6: x=x+30;
 case 5: x=x+31;
 case 4: x=x+30; 
 case 3: x=x+31;
 case 2: x=x+29;
 case 1: x=x+31;
}
if (t==0 && month>1) x=x-1;
 x=x+date;
 printf("为本年的第%d天",x);
}
#include <stdio.h>
main()
{
    int year,month,two,day,sum=0;//two代表2月 
    printf("请输入年份:"); 
    scanf("%d",&year);
    printf("请输入月份:");
    scanf("%d",&month);
    switch(month)
    {
        case 1:sum=0;break;
        case 2:sum=31;break;
        case 3:sum=59;break;
        case 4:sum=90;break;
        case 5:sum=120;break;
        case 6:sum=151;break;
        case 7:sum=181;break;
        case 8:sum=212;break;
        case 9:sum=243;break;
        case 10:sum=273;break;
        case 11:sum=304;break;
        case 12:sum=334;break;
        default:printf("输入错误"); 
    }
    printf("请输入日:");
    scanf("%d",&day);
    sum=sum+day;
    if(year%4==0&&year%100!=0||year%400==0&&month>2)
    sum++;
    printf("今天是%d年的第%d天\n",year,sum);    
 }